This mud pool near Wai-o-tapu is the result of nearby volcanic activity. Over time, volcanic ash and glass accumulate in a basin. These sediments are then converted to smectite by hot water. The hot water also is the result of volcanic activity; to the east in the Hikurangi Trough the Pacific plate is subducted under the Australian plate. This subduction creates a heat source for ground water. As the smectite is heated, it becomes less dense than the smectite and water around it causing it to rise to the surface, creating a bubbling mud pool. The water is so hot that it readily evaporates, causing steam to form on the surface. The hot water trapped in the rising smectite also can result in the release of steam at the surface.
Marine terraces typically form when the ocean sea level drops, the shoreline is raised, or a combination of the two. The last interglacial sea level should be about 20 meters above the present sea level; however you can see in this photograph at Turakirae Head that the marine terrace from this period is over 100 meters above the current sea level, indicating that substantial uplift has been occurring. In 1855 the coast was uplifted in some places to 7 meters, creating a new marine terrace. These terraces can be used to determine recurrence intervals of earthquakes in the surrounding area as well, which is very useful for insurance companies to determine premiums for natural disaster claims. Similar uplifts have been used in Papua New Guinea to determine sea level changes over time. Marine terraces are vital to the understanding of geological processes in the past and for predicting the future.
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